How to remove an item at a given index from Array/List in Elm?

Question

What is the most elegant way to remove an item at index i in a given Array? In a given List?

Answer 1

This should be pretty efficient:

remove : Int -> Array a -> Array a
remove i a =
  let
    a1 = Array.slice 0 i a
    a2 = Array.slice (i+1) (Array.length a) a
  in
    Array.append a1 a2

Answer 2

Best I could think of:

removeFromList i xs =
  (List.take i xs) ++ (List.drop (i+1) xs) 

removeFromArray i =
  Array.toList >> removeFromList i >> Array.fromList 

Answer 3

Use List.Extra.removeAt from elm-community.

Answer 4

I needed an indexedFilter function recently. This could provide you a fold based alternative

indexedFilter : (Int -> a -> Bool) -> List a -> List a
indexedFilter p xs =
    let
        tup = List.map2 (,) [ 0 .. List.length xs - 1 ] xs
    in List.foldr (\(i,x) acc -> if p i x then x :: acc else acc) [] tup